1. Field of the Invention
The present invention relates to polyimidosiloxane solution compositions which are mixtures of an organic solvent-soluble polyimidosiloxane, an epoxy resin and an organic solvent, and optionally also mica or barium sulfate, as well as to cured products thereof. The compositions have excellent storage stability, and may be suitably used for such purposes as printing inks and application varnishes to allow screen printing on flexible wiring boards, formation of protective films by using dispensers, etc.
When a polyimidosiloxane composition according to the present invention is applied onto a substrate in the form of a solution and allowed to dry and harden to form a protective film, the protective film has excellent flexibility (flexing resistance), heat resistance, adhesive properties, chemical resistance (particularly against soldering flux and tin plating solutions) and soldering resistance and is adherent to substrates, for example, polyimide film, copper foil, etc., allowing formation of an excellent protective film without requiring pretreatment of the substrate with a silane coupling agent or another adhesion accelerator.
2. Description of the Related Art
The use of aromatic polyimides, epoxy resins and the like in electrically insulating protective films has been known for such applications as solid-state insulating films, passivation films, and insulating films for semiconductor integrated circuits and flexible wiring boards.
Epoxy resins generally require the use of a curing agent, which has raised a number of problems including the storage stability of the curing agent and its manageability for two-pack preparations, and when used for insulating films as mentioned above, the insulating films formed by thermosetting are rigid, thus lacking flexibility.
Furthermore, since most polyimidosiloxanes are poorly soluble in organic solvents, it is necessary to use a solution of the polyimidosiloxane precursor (polyamic acid), as described in Japanese Unexamined Patent Publication (Kokai) Nos. 57-143328, 58-13631 and 2-11631, to form a coated solution layer, and then accomplish drying and imidation of the coated layer by prolonged high-temperature heating to form a polyimide protective film, which process has resulted in the problem of heat deterioration of the electronic material which is to be protected.
Polyimidosiloxanes soluble in an organic solvents are also known as described in Japanese Unexamined Patent Publication (Kokai) Nos. 61-118427, 61-207438, 63-225629, 1-121325, 2-91124, 4-23833 and 4-36321, but have disadvantages in that curl occurs in the flexible substrates, resistance to soldering flux is poor, and viscosity stability is poor.